In many cases, oilfield water produced in oil fields or gas fields includes hardly-degradable water-soluble organic substance (phenol, polycyclic aromatic hydrocarbons, or the like) or heavy metals as well as oil. Releasing of such oilfield water in an untreated state to the environment should be avoided. How to treat the oil, heavy metals, water-soluble organic substance, or the like contained in the oilfield water is an important problem.
As methods of removing the oil from oil-containing water, several methods have been proposed.
Patent Document 1 discloses a method where, in an oil-water separation apparatus for removing oil from water to be treated containing the oil, contained oil is emulsified by emulsion generating means or oil phase removing means, the resulting product is added with a magnetic powder and a flocculent to generate magnetic floc, and the magnetic floc is suctioned and separated by a magnetic force and is collected in the atmosphere.
Patent Document 2 discloses a waste water treatment method for crude oil containing exhausted water where, in waste water treatment for crude oil containing exhausted water exhausted from a crude oil mining process or the like, oil floating in a suspension state in the crude oil containing exhausted water is aggregated, precipitated, and separated by using an organic polymer flocculent, and the oil dissolved in the waste water is oxidized and decomposed by using the polymer flocculent and an oxidizing agent.
Patent Document 3 discloses a flocculation magnetic-separation system flocculates oil and solids (including heavy metals) in oilfield water by mixing a flocculent containing magnetic powder into the oilfield water and removes the oil and solids.
These methods can be used as a primary treatment method of removing the oil or the like from the oilfield water.
Even in the case where the oil and solids are removed from the oilfield water, the primarily treated water may contain a large amount of and various types of water-soluble organic substances. Therefore, how to treat these substances is a problem.
Patent Documents 4 and 5 address the problem, “although oil content of oilfield water is removed, a large amount of organic compounds, for example, acetic acid, propionic acid, valeric acid, and the like are still dissolved, and thus, these compounds cause malodor and damage to the environment, so that the removal thereof has been studied” and proposes a treatment method of removing the dissolved organic compounds contained in the oilfield water.
Patent Document 4 discloses a method of removing organic compounds dissolved in oilfield water where oilfield water obtained by separating crude oil from a mixture of the crude oil and brine is allowed to be in contact with an absorbent to absorb and remove the organic compounds dissolved in the oilfield water, and the absorbent is reproduced by desorbing the absorbed compounds from the absorbent.
Patent Document 5 discloses an oilfield water treatment method where oilfield water obtained by separating oil from crude oil water produced in mining of crude oil is allowed to be in contact with zeolite of which molar ratio of SiO2/Al2O3 is in a range of 100 to 200, so that dissolved organic compounds contained in the oilfield water are absorbed and removed.
Main purposes of the aforementioned methods in the related art are to separate and remove the dissolved organic substances by using the absorbent, and thus, there is a need to further treat the removed organic substance. In Patent Document 4, vaporization and removal of volatile organic compounds using an aeration apparatus is performed as a pre-treatment of the adsorption treatment, and heating and reproduction of the absorbent and combustion of the organic compounds in the exhausted gas is performed as a post-treatment of the adsorption treatment.
The present inventors have focused on discharge for the purpose of collectively treating oilfield water containing various types of organic substance (various types of water-soluble organic substances and various types of volatile organic substances), and seek to treat the oilfield water by an approach different from the method of adsorbing and removing the dissolved organic products.
In particular, since the oilfield water contains various types of organic substances according to mining sites, it is advantageous that these organic substances are collectively decomposed and removed.
Water treatment using discharge has already been known, and such water treatment is disclosed in, for example, Patent Document 6, Patent Document 7, and Patent Document 8. However, higher efficient treatment using a more compact, simpler apparatus is desired. In addition, but not limited to the oilfield water, it is desired to efficiently treat organic substances of water containing various types of hardly-degradable organic substances.
Patent Document 1: JP 2003-144805 A
Patent Document 2: JP 2004-255290 A
Patent Document 3: JP 2012-40536 A
Patent Document 4: JP 5098334 B
Patent Document 5: JP 2007-283203 A
Patent Document 6: JP 4073240 B
Patent Document 7: JP 2009-241055 A
Patent Document 8: JP 2012-236131 A